1. Field of the Invention
The present invention relates generally to a three-dimensional image processing apparatus, and more particularly to a three-dimensional image processing apparatus that forms a three-dimensional image by combining a plurality of two-dimensional tomographic images.
2. Description of Related Art
A tomographic image acquired by an X-ray computed tomography (CT) system consists of two-dimensional data composed of a matrix of lateral and longitudinal pixels. The number of each of lateral and longitudinal pixels is, for example, 512. The lateral direction of the tomographic image corresponds to the lateral direction of a subject (e.g., a human body), and the longitudinal direction of the tomographic image corresponds to the sagittal direction of the subject. A plurality of tomographic images is acquired by gradually shifting the measurement positions along the axis of the subject to thereby produce three-dimensional image data on the lateral direction, the sagittal direction and the axial direction of the subject. A conventional method for forming a three-dimensional image from the three-dimensional data comprises the steps of:
(i) acquiring two-dimensional data a plurality of times;
(ii) producing three-dimensional data from the two-dimensional data acquired at the step (i) and writing the three-dimensional data in a memory;
(iii) setting a viewpoint and rotating the three-dimensional data produced at the step (ii) according to the viewpoint; and
(iv) combining the data to compute three-dimensional pixel values.
If the two-dimensional data (reconstructed data) acquired by one measurement at the step (i) is d(x, y), the three-dimensional data produced at the step (ii) is d(x, y, z). The coordinates of pixels are transformed at the step (iii) as follows:
(x, y, z)xe2x86x92(xxe2x80x2, yxe2x80x2, zxe2x80x2),xe2x80x83xe2x80x83(1)
where zxe2x80x2 is a coordinate on the zxe2x80x2 axis, which is set along the sagittal direction from a viewpoint (e.g., at the front), and is the distance between the viewpoint and the pixel. In this case, only the coordinates are transformed, and the pixel values are unchanged. The three-dimensional data d(xxe2x80x2, yxe2x80x2, zxe2x80x2) is produced by the coordinate transformation. At the step (iv), the data are combined as expressed by the following equation to thereby compute a pixel value dz:
dz(xxe2x80x2, yxe2x80x2)=F{d(xxe2x80x2, yxe2x80x2, z1xe2x80x2), d(xxe2x80x2, yxe2x80x2, z2xe2x80x2), . . . , d(xxe2x80x2, yxe2x80x2, zmxe2x80x2)};xe2x80x83xe2x80x83(2)
where F is a combining function, and factors thereof are all the coordinate values Zxe2x80x2=z1xe2x80x2, z2xe2x80x2, . . . , zmxe2x80x2 where pixels of the zxe2x80x2-axis exist with respect to the coordinate (xxe2x80x2, yxe2x80x2). If there is no pixel at a point (xxe2x80x2, yxe2x80x2), the data is not combined for the point (xxe2x80x2, yxe2x80x2) in accordance with the equation (2), and it is determined that there is no pixel. If the pixel exists at only one point (xxe2x80x2, yxe2x80x2, z1xe2x80x2) a pixel value at this point (xxe2x80x2, yxe2x80x2, z1xe2x80x2) is selected as dz(xxe2x80x2, yxe2x80x2). In short, the data are combined according to the equation (2) only when the pixels exist at two or more points. For example, if the depth projection method is used, the combining function F selects only a pixel value at the coordinate value z1xe2x80x2 of the zxe2x80x2-coordinate that is closest to the viewpoint among the coordinate values zxe2x80x2=z1xe2x80x2, z2xe2x80x2, . . . , zmxe2x80x2. The combining function F processes the data so that the closer (smaller) the coordinate value zxe2x80x2 is, the larger the pixel value dz is and that the farther (larger) the coordinate value zxe2x80x2 is, the smaller the pixel value dz is. For example, the combining function F is represented as:
dz=D/zxe2x80x2;xe2x80x83xe2x80x83(3)
or
xe2x80x83dz=Dxc2x7(1xe2x88x92zxe2x80x2)xe2x80x83xe2x80x83(4)
where zxe2x80x2 is the zxe2x80x2-coordinate of the closest pixel, and D is the set pixel value when zxe2x80x2=0. dz(xxe2x80x2, yxe2x80x2) is found for every coordinate (xxe2x80x2, yxe2x80x2) to produce three-dimensional data. The three-dimensional data are displayed on a two-dimensional screen to thereby complete a three-dimensional image.
FIG. 10 shows the conventional procedure for forming a three-dimensional image. In the conventional measurement, two-dimensional images (#1-#6) are outputted every time the measurement positions are updated like P1 (the starting position)xe2x86x92P2xe2x86x92 . . . xe2x86x92P6. After all the images (#1-#6) are reconstructed as a result of the measurements, the three-dimensional image forming processing is started, and the images (#1-#6), which are recorded in the measurements, are read out (the processing A), and they are rotated according to the viewpoint (the processing B). Then, the data are combined in accordance with the combining function to thereby complete a three-dimensional image.
In the conventional procedure, however, the three-dimensional image is ordinarily formed after the acquisition of the two-dimensional data and the reconstruction of the two-dimensional images are completed. Thus, the conventional procedure cannot satisfy the need for outputting a three-dimensional image in real-time during the acquisition of the two-dimensional data (for example, when the acquisition of the data relating to the image #3 is finished in the case that the images #1-#6 are used to form the complete three-dimensional image). Since all the two-dimensional images are used to form the three-dimensional image after the reconstruction of the two-dimensional images, the waiting time until the completion of the three-dimensional image is so long that the efficiency of the imaging diagnosis is decreased.
In view of the forgoing, it is an object of the present invention to provide a three-dimensional image processing apparatus that enables a high-speed processing by producing three-dimensional images in real-time during the acquisition of two-dimensional data.
To achieve the above-mentioned object, the present invention is directed to a three-dimensional image processing apparatus, comprising: a measurement position setting device which sets a plurality of measurement positions in a predetermined order in a predetermined direction of a subject; a measurement data collecting device which collects measurement data of the subject at the plurality of measurement positions; a two-dimensional image data acquiring device which acquires two-dimensional image data from the measurement data at the plurality of measurement positions in the predetermined order; a three-dimensional image data producing device which produces, every time the two-dimensional image data acquiring device acquires latest two-dimensional image data, three-dimensional image data on the basis of the latest two-dimensional image data and two-dimensional image data acquired before the latest two-dimensional image data; and a display which displays the three-dimensional image data as a three-dimensional image every time the three-dimensional image data producing device produces the three-dimensional image data.
To achieve the above-mentioned object, the present invention is also directed to a three-dimensional image processing apparatus, comprising: a measurement position setting device which sets a plurality of measurement positions in a predetermined order in a predetermined direction of a subject; a measurement data collecting device which collects measurement data of the subject at the plurality of measurement positions; a two-dimensional image data acquiring device which acquires two-dimensional image data from the measurement data at the plurality of measurement positions; and a three-dimensional image data producing device which produces three-dimensional image data on the basis of the two-dimensional image data at the plurality of measurement positions, the three-dimensional image data producing device producing three-dimensional image data in a measurement area corresponding to the plurality of measurement positions set by the measurement position setting device by combining three-dimensional image data produced on the basis of two-dimensional image data at a measurement position that is set before the finally set measurement position among the plurality of measurement positions and two-dimensional image data at the finally-set measurement position while the measurement data collecting device is measuring the measurement data.
According to the present invention, the plurality of measurement positions is set in the predetermined direction of the subject in the predetermined order, and the two-dimensional image data acquiring device acquires the two-dimensional image data at the plurality of measurement positions. The three-dimensional image data producing device produces the three-dimensional image data at the finally-set measurement position by combining the three-dimensional image data at the measurement position that is set at the predetermined distance from the finally-set measurement position, with the two-dimensional image data at the finally-set measurement position.
Preferably, the apparatus further comprises a display which displays the three-dimensional image data, produced by the three-dimensional image data producing device, as a three-dimensional image. This enables the real-time display of the three-dimensional image data on the display during the acquisition of the two-dimensional image data.